Filter auto-created device list if user namespaces enabled
Filter auto-created device list if user namespaces enabled

Because devices will be bind-mounted instead of using `mknod`, we need
to make sure the source exists and filter the list by only those whose
source is a valid path/current device entry.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)

(cherry picked from commit 9a554e8c37d522ed791b3bb55f9ba9f21e2ac76a)

swasd/baleno,swasd/baleno,swasd/baleno